TEKS-Based Activity Starter for Grade 8
Square Dancing
Description
This learning experience is designed to teach students to use Punnett squares to
predict the genotype and phenotype of offspring from given parents.
Time Frame
1–2 lessons (45 minutes each)
Correlation to Texas Essential Knowledge and Skills
During this activity, students will be exposed to the following Texas Essential
Knowledge and Skills:
Note: Some TEKS statements below end with a ; or and and nothing thereafter—
this indicates that further TEKS statements follow but are not included here.
(8.11) Science concepts. The student knows that traits of species can change
through generations and that the instructions for traits are contained in the genetic
material of the organisms. The student is expected to:
(C)
make predictions about possible outcomes of various genetic
combinations of inherited characteristics.
Note: The TEKS listed here are the main content TEKS for this activity;
however, this activity may also cover additional content and process skills
included in other TEKS.
Materials
Colored plastic squares (about 2 cm x 2 cm; 10 per student group)
Clear plastic squares (about 2 cm x 2 cm; 10 per student group)
Lunch-size paper bag (1 per student group)
Square Dancing student investigation pages (included at the end of this activity)
Materials note: It does not matter what color the plastic squares are; however,
all the colored plastic squares must be the same color. Alternatives to the plastic
squares include clear and colored game chips, or transparency sheets cut into
squares (either use colored transparency sheets or color the sheets with a colored
permanent marker). If you do not use the plastic squares, revise the student
investigation pages to reflect the change.
Background Information for the Teacher
A Punnett square is used to model the probability of gene combinations resulting
from the cross between two organisms. It was developed by Reginald Crundall
Punnett, a British geneticist. The Punnett square works much like a
multiplication table, except that a Punnett square has no numbers. For example,
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TEKS-Based Activity Starters
Grade 8—Square Dancing
look at the two squares below. The first square is a multiplication table, and the
second square is a Punnett square.
In the first square, what numbers belong in the box with the question marks?
[7 x 4]
In the second square, what belongs in the box with the question mark?
[Rr]
Punnett squares are laid out so that the alleles of the female are across the top and
labeled using the symbol for the planet Venus. Each column is labeled with one
of the two letters representing the female’s two alleles (in the second Punnett
square it is RR). The alleles of the male are down the left side and labeled using
the symbol for the planet Mars. Each row is labeled with one of the two letters
representing the male’s two alleles (in the second Punnett square it is Rr).
When the male and female alleles are “multiplied,” the resulting combination of
the two alleles gives the possible genotypes of the offspring. These genotypes
can be used to predict the phenotypes of the offspring. For phenotypes in pea
plants, R represents a smooth seed, while r represents a wrinkled seed. In the
Punnett square above, every possible offspring has at least one dominant allele,
R. Therefore, it can be said the offspring have a 2 out of 4, or 50%, chance of
having a heterozygous genotype. There is a 0 out of 4, or 0%, chance of an
offspring being homozygous recessive.
The Punnett square will look like the square below if both the female and the
male parents are heterozygous. In this example, there is a 25% chance that the
offspring will have the homozygous genotype of RR, a 50% chance that the
offspring will have the heterozygous genotype Rr, and a 25% chance that the
offspring will have the homozygous genotype rr. The possible phenotypic ratio is
that three-fourths of all seeds will be smooth and one-fourth of all seeds will be
wrinkled.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
If the female is homozygous recessive and the male is heterozygous dominant,
the Punnett square will look like the square below. In this example, there is a
50% chance that the offspring will have a homozygous genotype of rr, and a
50% chance that the offspring will have the heterozygous genotype of Rr. The
homozygous genotype RR does not occur. The phenotypic ratio is that half of all
seeds will be smooth and half of all seeds will be wrinkled.
Note: It is very important to emphasize to students that a Punnett square is used to
determine a ratio or a percentage. The ratio or percentage is a probability that some
thing will happen. Make sure students understand that the square does not indicate
that four offspring are produced. It is important to be aware of how we say things.
For example, telling students that 1 of 4 offspring will be heterozygous implies that
there are always four offspring. Instead, tell students that there is a 1-out-of-4
chance that any offspring could be heterozygous.
Advance Preparation
Make a copy of the student investigation pages for each student group.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
Procedures
1. Using the blue and clear plastic squares and the transparency, show students
how a Punnett square functions by demonstrating the examples found in the
background information of this learning experience. Ask students to name
the genotype (letters) and phenotype (flower color) of the offspring.
2. Have students identify the probability of each possible genotype and/or
phenotype by holding up the correct number of fingers as you ask questions
such as, “What is the probability of heterozygous offspring?” If it were 2 out
of 4, for instance, students might hold up two fingers on the right hand and
four fingers on the left hand. Instead of asking the entire class to answer,
consider using index cards with students’ names on them so you can
randomly select students to answer.
3. Give each student group the Square Dancing student investigation pages and
two paper bags: one containing blue squares and one containing clear squares.
4. Have each group use the blue and clear squares to complete step 1 in the
student investigation pages.
5. Explain to students that a pedigree illustrates lineage or ancestor
relationships. Draw on the board the pedigree illustrating the crosses between
a blue flower and a white flower with the following offspring.
Leave the genotypes out of the pedigree for now. Have students complete
step 2 in the student investigation pages—listing possible genotypes for the
parents and the offspring. Discuss the possible genotypes as a whole class
and fill in the correct genotypes on the board, as shown above.
6. Have students complete step 3 in the student investigation pages, for which
they will construct a pedigree illustrating the cross between two blue flowers,
resulting in five blue-flowered offspring and two white-flowered offspring.
Below is an example of what this pedigree should look like.
6. Ask student groups to answer the questions in the student investigation
pages. A guide to student responses is provided below.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
Guide to Student Responses
1. Which parent’s genotype is placed across the top of the Punnett square?
[female]
2. Which parent’s genotype is placed down the side of the Punnett square?
[male]
3. If you crossed two homozygous dominant blue flowers (BB), how many
flowers would probably be white out of 100 offspring?
[zero]
How many flowers would probably be blue?
[100]
4. If you crossed two heterozygous blue flowers (Bb), out of 100 offspring, how
many offspring would probably produce white flowers?
[25]
How many offspring would probably produce blue flowers?
[75]
5. What are the possible genotypes of the offspring from question 4?
[Bb, BB, or bb]
6. What are the possible phenotypes of the offspring from question 4?
[blue or white]
7. What does a pedigree illustrate?
[lineage or ancestor relationships]
Extension: Have students research the development of the maroon variety of
bluebonnets by Texas A&M University.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
Square Dancing
Student Investigation Pages
Description:
This learning experience is designed to help you use Punnett squares to predict the
genotype and phenotype of offspring from given parents.
Materials:
Paper bag containing blue plastic squares
Paper bag containing clear plastic squares
1. Follow the teacher’s directions and create Punnett squares for each of the crosses
listed below. Fill in the information requested for each square.
a. A cross between two homozygous dominant individuals.
Identify the expected genotypes and phenotypes of the offspring.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
Express the results in terms of a ratio (for example, a 2-out-of-4 chance that the
offspring will be __?) and in terms of a percentage (for example, a 50% chance
that the offspring will be __?).
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
b. A cross between a homozygous dominant male and a heterozygous female.
Identify the expected genotypes and phenotypes of the offspring.
Express the results in terms of a ratio and in terms of a percentage.
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
c. A cross between a homozygous dominant female and a heterozygous male.
Identify the expected genotypes and phenotypes of the offspring.
Express the results in terms of a ratio and in terms of a percentage.
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
d. A cross between two heterozygous individuals.
Identify the expected genotypes and phenotypes of the offspring.
Express the results in terms of a ratio and in terms of a percentage.
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
e. A cross between a heterozygous male and a homozygous recessive female.
Identify the expected genotypes and phenotypes of the offspring.
Express the results in terms of four a ratio and in terms of a percentage.
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
f. A cross between a heterozygous female and a homozygous recessive male.
Identify the expected genotypes and phenotypes of the offspring.
Express the results in terms of a ratio and in terms of a percentage.
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
g. A cross between two homozygous recessive individuals.
Identify the expected genotypes and phenotypes of the offspring.
Express the results in terms of a ratio and in terms of a percentage.
Determine if the cross will produce offspring that are consistently like the
parents, or offspring that may or may not look like the parents.
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TEKS-Based Activity Starters
Grade 8—Square Dancing
2. Look at the pedigree your teacher drew on the board. List all possible genotypes for
the parents and the offspring.
3. Construct a pedigree illustrating the cross between two blue flowers, resulting in five
blue-flowered offspring and two white-flowered offspring.
Questions:
1. Which parent’s genotype is placed across the top of the Punnett square?
2. Which parent’s genotype is placed down the side of the Punnett square?
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TEKS-Based Activity Starters
Grade 8—Square Dancing
3. If you crossed two homozygous dominant blue flowers (BB), how many flowers would
probably be white out of 100 offspring?
How many flowers would probably be blue?
4. If you crossed two heterozygous blue flowers (Bb), out of 100 offspring, how many
offspring would probably produce white flowers?
How many offspring would probably produce blue flowers?
5. What are the possible genotypes of the offspring from question 4?
6. What are the possible phenotypes of the offspring from question 4?
7. What does a pedigree illustrate?
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